Plasma arc torches are widely used for high temperature processing (e.g., heating, cutting, gouging and marking) of materials. A plasma arc torch generally includes a torch head, an electrode mounted within the torch head, an emissive insert disposed within a bore of the electrode, a nozzle with a central exit orifice mounted within the torch head, a shield, electrical connections, passages for cooling, passages for arc control fluids (e.g., plasma gas) and a power supply. A swirl ring can be used to control fluid flow patterns in the plasma chamber formed between the electrode and the nozzle. In some torches, a retaining cap is used to maintain the nozzle and/or swirl ring in the plasma arc torch. In operation, the torch produces a plasma arc, which is a constricted jet of an ionized gas with high temperature and sufficient momentum to assist with removal of molten metal. Gases used in the torch can be non-reactive (e.g., argon or nitrogen), or reactive (e.g., oxygen or air).
Design considerations for a plasma arc torch include features for cooling, since a plasma arc generated can produce temperature in excess of 10,000° C., which, if not controlled, can destroy the torch, particularly the nozzle. That is, the erosion rate of a nozzle is affected by the cooling efficiency at the nozzle. Efficient cooling can help to maintain a relatively low temperature, which leads to a lower erosion rate. Prior art nozzles, such as the nozzles described in U.S. Pat. No. 8,772,667, include a toroidal chamber configured to allow fluid flows through and along the chamber to promote convective cooling of the nozzle. Specifically, a fluid enters the chamber from one side of the nozzle, flows around the nozzle within the chamber to the other side of the nozzle, and exits the nozzle from the opposite side of the nozzle. Such convective cooling tends to promote turbulence in the fluid flow and results in unevenness in cooling as the cooling fluid enters one side of the nozzle and exit from the opposite side at a warmer temperature. There is a need for nozzle cooling features that can provide smooth, laminar fluid flows while enabling uniform cooling around substantially the entire circumference of the nozzle.